A communication system transfers information between a source and a destination. Generally, a communication system includes a transmitter and a receiver which transmit and receive information signals over some media. This media may be cable wiring or atmosphere. When communications occur over atmosphere, or airwaves, they are commonly referred to as "wireless" communications. Examples of wireless communication systems include digital cellular, packet data, paging and digital cordless telephones, wireless modems, wireless local and wide area networks, digital satellite communications and personal communications networks.
Inherent in some wireless communications systems is equipment mobility. In other words, since the communication media is air, wireless communications equipment may be portable. If the equipment is portable, this communication equipment must provide its own source of power, such as a battery unit. Typical batteries used in portable devices may include AA batteries or AAA batteries producing 1.5 volts. In other portable devices, batteries such as Nickel Cadmium (NiCd) battery cells and lithium-ion battery cells may be used.
One problem with the AA or AAA batteries is that because of their internal series resistance and low voltage, they cannot satisfy the power requirements for certain portable devices. For example, a transmitter in a communications device may require a high voltage and high current power source to supply bursts of power to function, typically one that generates 3 to 5 watts of power. A 1.5 volt AA battery cannot generate this much power.
One solution for generating more power in a device is to increase the size or number of batteries used to power the portable device. However, space in portable devices is usually at a premium, and the battery size that may be used is often limited to the space available. A non-rechargeable battery of the size necessary to produce, for example, 3 to 5 watts, is much larger in size than the current batteries used in the portable devices. Therefore, it is desirable to generate the necessary power. In a device using as little space within the unit as possible.
Another solution for generating more power in a portable system is to use a capacitive discharge system wherein a capacitor is charged such that it discharges power at the desired wattage. There are problems with using a capacitive discharge system in portable devices. For instance, either the size of the capacitors which are required are prohibitive given the size constraints of the portable devices or existing capacitors have too much internal resistance. Even though the capacitors have enough capacity to power short transmitter bursts, they do not have enough capacity to power amplifiers in a transmitter for the time required to send a short message, particularly at low data rates typically used in portable wireless communications systems. Also, capacitive discharge systems cannot accommodate worst case duty cycles where a transmitter or other device is repeatedly placed on and off for short periods of time. That is, a single capacitor could not provide bursts of power for a short period of time and then recharge fast enough for currently desired duty cycles. Therefore, using a capacitor discharge scheme limits the size of data packets that could be sent and the time between data packets has to be lengthened to accommodate intervening recharge cycles.
The present invention provides a technique to generate high-current pulses in a small area. This allows the size of a transmitter to be miniaturized specifically for certain applications.